In the file manager you can see the files you have uploaded and the lists you have created.
By clicking the search bar or pressing the / button you can search through your files or lists. Only the entries matching your search term will be shown. Pressing Enter will open the first search result in a new tab. Pressing Escape will cancel the search and all files will be shown again.
With the Select button you can click files to select them. Once you have made a selection you can use the buttons on the toolbar to either create a list containing the selected files or delete them.
Holding Shift while selecting a file will select all the files between the file you last selected and the file you just clicked.